Spark plug



Feb. 5, 1963 E. J. NovAK ETAL SPARK PLUG Filed Jan. 8. 1959 SN KS lllllllllll FIG F/A RATIO LEAN . msommwmoz wvmm LEAN 1- F/A RATIO RICH 1N VENTORS EMIL J. NOVAK PAUL F. ADAlR 3,675,912 Patented Feb. 5, 1963Sdi'ol?. SPARK PLUG Emil 5. Novak, Laureiton, and Paul F. Adair,Commaca, NY., assiguors to .let ignition Co., inc., Mineola, ion-gisland, New York, a corporation oi' New Yori;

Filed dan. 8, 1959, der. No. 765,7@ 4 Claims. (Cl. 315-4143) The presentinvention relates to spark plugs, and particularly to a new and improvedspark plug that possesses a maximum brake horsepower characteristic overa relatively large but preselected range of varying fuel-air ratios.

Commonly known open-faced spark plugs possess a peaked curve brakehorsepower characteristic when enrployed with varying fuel-air ratios.There is a single point throughout a range of fuel-air ratios at whichmaximum brake horsepower is available. Greater and lesser fuel-airratios relative to this point are atten-ded with a substantial decreasein available brake horsepower and, consequently, lower eiiiciencies ofengine operation.

The tip of the insulation that supports the central terminal of suchopen-faced plugs is cyclically subjected to wide temperature variations,causing excessive fouling due to carbon deposits, pre-ignition, and leaddeposits at the higher temperatures. Consequently, such plugs seldomoperate within the most elcient operating temperature range.

In order to more clearly deline the present invention, the followingdefinitions are relied upon insofar as the present invention isconcerned:

(l) The heat rating characteristic of a spark plug is the pounds persquare inch of indicated mean effective pressure (Ll/LBP.) at which thespark plug will operate without pre-ignition occurring.

(2) The most eiicient operating temperature or heat range through whichthe insulating tip should cycle means a range of temperatures wherein attemperatures below the low of the range, excessive fouling occurs due tocarbon deposits on the tip; and wherein at temperatures above the highof the range, lead deposits and pre-ignition occur. It has been foundthat the most efcient temperature range is approximately from about 960F. to approximately 1200 F.

(3) The mixture response of a spark plug means the fuel-air ratio inrelation to the maximum brake horsepower that can be developed.

(4) A hot rated plug is one rated low on the LME?. scale and which canonly operate at relatively low power output without pre-ignitionoccurring.

(5) A cold rated plug is one rated high on the LMEP. scale and which canoperate at high power output Without pre-ignition.

Attempts have been made vto produce spark plugs having a maximum brakehorsepower over a relatively large range of varying fuel-air ratios, andthese 'have for the purposes intended produced the results for whichthey were designed. Such a spark plug is shown, described and claimed inPatent No. 2,895,069, issued July 14, 1959, in the name of Putnam Davis.Spark plugs of this type usually include a body containing an ignitionchamber within which spaced electrodes form a spark gap and ingress andegress of the fuel-air mixture as well as the burning gases afterignition occur through helical passages providing a swirling action tothe fuel and gases. Such plugs, for the purpose of this application andto distinguish them from the open-faced plugs, will be referred tohereinafter as chamber-type plugs. These chamber-type plugs have a brakehorsepower characteristic that essentially follows that of the commonlyknown open-faced plug to a point where maximum brake horsepower isproduced with a given fuel-air mixture. As the fuel-air mixture isincreased. or becomes richer, the available brake horsepower of theopen-faced plug rapidly decreases, whereas that of the chamber-type plugremains at a maximum for an extended range of: fuel-air ratios.

It has become increasingly important to provide Spark plugs capable ofuse under diterent conditions that will produce a maximum brakehorsepower characteristic over a preselected range of fuel-air ratios.Thus, in aircraft and passenger automobile use, a relativ-ely richfuelair mixture is desirable at take-olf or start, and immediately uponmoving, the aircraft and automobile preferably should operate on a muchleaner mixture. Employing either the commonly known open-faced plug orthe chamber-type having the characteristics above outlined causes powerloss when the fuel-air ratio is varied toward a leaner condition.

The most eiiicient operating temperature range of a spark plug hasbecome recognized as an important consideration in engine eiiiciency. Inchamber-type plugs, this temperature range is controlled by the volumeof the separate chamber within which ignition initially occurs,excluding the volume of the electrode supporting porcelain extendinginto said chamber. Accordingly, by varying this differential volume, aseries of plugs can be designed having any desired heat ratingcharacteristic.

The principal object of this invention is to provide a spark plug havinga maximum horsepower characteristic over a relatively large preselectedrange of fuel-air ratios.

Another object of the invention is to provide a series of spark plugshaving a predetermined heat rating and in addition a maximum brakehorsepower characteristic over` a relatively large preselected range offuel-air ratios.

Another object of this invention is to provide a wide range of sparkplugs covering a Wide range of heat ratings as well as a wide range ofmixture response, and wherein said plugs will possess the most eiiicientoperating ternerature range through which the insulating tip will cycle.

Another object of the invention is to provide a series of spark plugshaving different heat ratings and which will operate to maintain in thevicinity of the spark gap, a fuelair mixture of as near best powermixture as possible. Y

Another object of this invention is to provide a series of spark plugshaving diiferent heat ratings and which, when used with enginespreferring a rich mixture during normal operation, will tend toautomatically reduce the richness of the fuel-air mixture in thevicinity of the spark gap.

Another object of this invention is to provide a series of spark plugshaving different heat ratings and which, when used with enginespreferring a lean mix-ture during normal operation, willvtendautomatically to enrich the fuel-rich mixture in the vicinity of thespark gap.

g in one aspect of this invention, the body of the spark plug may beprovided with a chamber for receiving the usual electrode supportingporcelain. The chamber may be clos-ed at its end that is adapted toextend into a cylinder of an internal Combustion engine. 1Helicalpassages, or passages to produce a simiiareffect, may be providedbetween the interior of the chamber and the exterior of the closed endfor imparting a swirling action to the gases that pass therethroughduring the compression stroke of the engine, and to the burning gasesafter ignition takes place within the chamber.

In another aspect of the invention, means may be provided within thechamber for automatically controlling the fuel-air mixture adjacent thespark gap. In the embodiment disclosed, this means takes the form of anannular element which may be integrally 'fixed at different locationswithin the chamber. Since the most etlicient operating temperature rangeof a plug is controlled by the volume of the chamber less the volume ofthe electrode supporting porcelain extending thereinto, this rnostefficient range may be provided by employing different length and/ordifferent inside diameter annular elements, as well as by varying thecapacity of the chamber farthest from the spark gap that i's formed bythe annular element. Once a design has been established with a givenchamber size and annular element size, varying the location of theannular element within the chamber makes it possi-ble to vary thefuel-air mixture response of the plug.

Accordingly, in another aspect of the invention the annular element maybe iixed to the side wall of the chamber at different locations,providing separate compartments within said chamber which combine withthe swirling action of the gases to vary the fuel-air mixture responseof the plug.

The above, other objects and novel features of the invention will becomeapparent from the following spec-iiication and accompanying drawingwhich is merely exemplary. In the drawing:

FIG. 1 is a sectional elevational view of a prior art chamber-type plug;

FIG. 2 is a sectional elevational view of a chambertype plug for usewith engines preferring a richer than best power fuel-air mixture fornormal operation, and to which the principles of the invention have beenapplied;

FIG. 3 is a sectional elevational view of a plug similar to that of FIG.2 but designed for use with engines preferring a leaner than best powerfuel-air mixture for normal operation, and to which the principles ofthe invention have been applied;

FIG. 4 is a graph of the brake horsepower characteristics of the plugsof FIGS. l and 2 in relation to that of a conventional open-faced plug;and

p FIG. 5 is a graph of the brake horsepower characteristics of the plugof FIG. 3 in relation to that of a conventional open-faced plug.

Referring to the drawing, and particularly to FIG. 1, a conventionalchamber-type spark plug may comprise a substantially cylindrical metalbody 1t) having its end which is adapted to extend into a cylinder of aninternal 'combustion engine closed by a plate element 11 which supportsone electrode 12 of the igniter system. The usual insulator element 13is mounted within the body 1G and is held therein by the usual nut 14.The insulator element 13 supports the other electrode 15 of the ignitersystem, to the outer end of which the usual terminal 16 is fixed.

Helical passages 17 may be provided in the body 1t?, providingcommunication between a chamber 1S surrounding the spark gap 19 and theinterior of a cylinder with which the plug is employed.

It has been found that if a spark plug is caused to cycle throughout themost eihcient operating temperature range, the insulator nose will bemaintained free from conductive deposits which, due to their lowerresistance than that of the normal air or spark gap, tend to flash over,causing loss of normal ignition.

Referring to FIG. 2, the principles of the present invention are shownin one form as applied to a plug similar to that shown in FIG. 1. Inthis disclosure, a plug of a desired heat rating has been designed foruse with an engine which under normal operation prefers a fuel-airmixture that is richer than best power. Such engines are those fortrucks, marine, industrial use and the like. The chamber 18 of the plugin FIG. 2 may include an annular element 20 that is shown as a sleevethat may permanently be fixed to the side wall of the chamber 1S incontact with the end plate 11. This element 20 may be provided in anyone of several forms such as by boring and counterboring the chamber 18,or forging the annular element at apredetermined location within chamber1S.

Tests have indicated that the portion of the insulator or ceramic nosewhich is positioned adjacent to the sleeve element 20 may be caused tocycle throughout the most desirable temperature range and preventconductive deposits from forming thereon by virtue of the annularclearance between the sleeve and the insulator nose. in fact, for aspecic sleeve 2o having a specific annular nose clearance, the chamberconstruction to provide the most effective operating temperature rangeof the plug may be foundby varying the volume of the chamber farthestfrom the spark gap. rhis may be accomplished by counterboring thischamber to increase its capacity, which causes a greater volume of highvelocity gases to pass over the insulator nose without materiallychanging the basic heat rating characteristics of the complete plug.Accordingly, by the selection of correct dimensional sleeves 20 andchamber displacement combinations for a given heat rating, a maximumlinear insulator nose cleaning effect may be obtained, therebypreventing conductive deposits from occurring on the insulator nose.

During the compression stroke of the engine, the fuelair mixture, whichis richer than best power and therefore contains a greater portion offuel particles than a leaner mixture, is given a swirling or centrifugalaction with a force component directed away from the spark gap 19 as itis forced under high pressure through the helical passages il.Accordingly, the heavier fuel particles tend to be thrown away from thespark gap 19 into the portion 2.1 of the chamber 18, thereby providing aleaner fuel-air mixture in the vicinity of the spark gap 12.Accordingly, as the fuel-air mixture becomes richer and richer, thespark gap is surrounded by a fuel-air mixture that remains in thevicinity of the best power mixture, thus producing a relatively longrange of maximum brake horsepower with increasing fuel-air ratios.

Referring to FIG. 4, the dotted line curve represents the brakehorsepower characteristic of the conventional openfaced spark plug. Thiscurve has a single point 22 of maximum brake horsepower. Variations offuelair ratio above and below this point are attended with rapid loss ofbrake horsepower and consequent ineiiicient engine operation. The solidline curve of FIG. 4 represents the brake horsepower characteristics ofthe chamber-type plug of FlGS. 1 and 2, and the increase in range ofmaximum brake horsepower is due, at least in part, to the previouslydescribed structure of the chamber-type plug. From a review of FIGS. l,2 and 4, it is evident that the prior known chamber-type plug hasparticular value when used with engines preferring, d-uring normaloperation, a fuel-air mixture richer than best power. However, if anengine prefers, during normal operation, a fuel-air mixture leaner thanbest power, the plugs of FIGS. l and 2 would produce a substantial fallin the available brake horsepower.

Referring to FIG. 3 wherein a chamber-type plug has been shown for usewith an engine preferring a fuel-air mixture leaner than best power, thesleeve or annular element 2t) has been relocated within the chamber 18so as to provide not only a compartment 2l. a substantial distance awayfrom the spark gap 19, but also a compartment 22 surrounding the airgap. During the compressio-n stroke of the engine, the leaner fuel-airmixture is again given a swirling centrifugal action, but in this casethe heavier fuel particles are thrown outwardly by centrifugal force andtend to be trapped and to be built up in concentration within thecompartment 22 while the lighter fuel particles pass outwardly into thecompartment 21. In this way the fuel-air mixture in the vicinity of theair gap 19 tends to be nearer best power even though a leaner than bestpower mixture is being used.

Referring to FIG. 5, it is evident that the solid line curverepresenting the brake horsepower characteristic of the plug of FIG. 3has shifted relatively to the dotted line curve from a longer range ofmaximum brake horsepower in a direction of increasing fuel-air ratio-sto a longer range of such horsepower in a direction of decreasingfuel-air ratios.

Since the most efficient operating temperature range of a chamber-typeplug is controlled by the free volume of chamber 18, and this freevolume does not vary with varying positions of the annular element 2i)Vwithin the chamber 18, it follows that the design of a chamber-type plugfor a given heat rating can be made in which the annular element 20 istaken into consideration. Then, a set of plugs having a given, unvaryingheat rating may Ibe provided with varying fuel-air mixture response froma lean to a rich response with any number of desired in` termediateresponse values therebetween and still all of the plugs will possess thesame most efficient operating range throughout which the insulator nosewill cycle without carbon fouling or lead deposit or pre-ignitionoccurring.

Although the various features of the new and improved spark plug havebeen described in detail to fully disclose one embodiment of theinvention, it will be evident that numerous changes may be made in suchdetails and certain features may be used without others withoutdeparting from the principles of the invention.

What is claimed is:

1. A spark plug comprising a hollow body having an internal spacedefining an ignition chamber, the free volume of which provides apredetermined heat range for said spark plug; a closure for said chamberat the end of said spark plug that communicates with the interior of anengine cylinder; spaced apart electrodes Within said chamber forming aspark gap; means providing ingress and egress of gases from said enginecylinder to said chamber; and a member within said chamber forming acompartment of substantially constant cross section extending asubstantial distance beyond said spark gap in each direction formaintaining the fuelair mixture surrounding said spark gap atsubstantially best power mixture when said fuel-air mixture is differentfrom best power mixture, said member Within said chamber being adaptedto be located in different posi- Itions within said chamber withoutmaterially affecting said heat range of said spark plug.

2. A spark plug comprising a hollow body having an internal spacedefining an ignition chamber, the free volume of which provides apredetermined heat range for said spark plug; a closure for said chamberat the end of said spark plug that communicates with the interior of anengine cylinder; spaced apart electrodes within said chamber forming aspark gap; means providing ingress and egress of gases from said enginecylinder to said chamber; and a member within said chamber forming anentrapping compartment of substantially constant cross section extendinga substantial distance beyond said spark gap in each direction formaintaining the fuel-air mixture surrounding said spark gap atsubstantially best power mixture when said fuel-air mixture is richerthan best power mixture, said member within said chamber being adaptedto be located in diiferent positions within said chamber withoutmaterially aifecting said heat range of said spark plug.

3. A spark plug comprising a hollow body having an internal space`delining an ignition chamber, the free volume of which provides apredetermined heat range vfor said spark plug; a closure for saidchamber at the end of said spark plug that communicates with theinterior of an engine cylinder; spaced apart electrodes within saidchamber forming a spark gap; helical passages extending from theinterior of said chamber to the exterior of said closure to provideingress and egress of gases from said engine cylinder to said chamber;and a mem-ber within said chamber forming a compartment of substantiallyconstant cross section extending a substantial distance beyond saidspark gap in each direction for maintaining the fuel-air mixturesurrounding said spark gap at substantially best power mixture when saidfuelair mixture is different from best power mixture, said means withinsaid chamber being adapted to be located in dierent positions withinsaid chamber without materially affecting said heat range of said sparkplug.

4. A spark plug comprising a hollow body having an internal spacedefining an ignition chamber, the free volume of which provides apredetermined heat range for said spark plug; a closure for said chamberat the end of said spark plug that communicates with the interior of anengine cylinder; spaced apart electrodes within said chamber forming aspark gap; helical passages extending from the interior of said chamberto the exterior of said closure to provide ingress and egress of gasesfrom said engine cylinder to said chamber; and a member within saidchamber forming an entrapping compartment of substantially constantcross section extending a substantial distance beyond said spark gap ineach direction for maintaining the fuel-air mixture surrounding saidspark gap at substantially best power mixture when said fuel-air mixtureis richer than best power mixture, said member within said chamber beingadapted to be located in different positions within said chamber withoutmaterially aecting said heat range of said spark plug.

References Cited in the le of this patent UNITED STATES PATENTS1,242,375 Robinson Oct. 9, 1917 1,361,580 Herz Dec. 7, 1920 2,060,340OMarra Nov. 10, 1936 2,127,513 Harper Aug. 23, 1938 2,497,862 Chuy Feb.21, 1950 2,519,273 Mitchel Aug. 15, 1950 2,642,054 Wright llune 16, 19532,646,782 Fisher July 28, 1953

2. A SPARK PLUG COMPRISING A HOLLOW BODY HAVING AN INTERNAL SPACE DEFINING AN IGNITION CHAMBER, THE FREE VOLUME OF WHICH PROVIDES A PREDETERMINED HEAT RANGE FOR SAID SPARK PLUG; A CLOSURE FOR SAID CHAMBER AT THE END OF SAID SPARK PLUG THAT COMMUNICATES WITH THE INTERIOR OF AN ENGINE CYLINDER; SPACED APART ELECTRODES WITHIN SAID CHAMBER FORMING A SPARK GAP; MEANS PROVIDING INGRESS AND EGRESS OF GASES FROM SAID ENGINE CYLINDER TO SAID CHAMBER; AND A MEMBER WITHIN SAID CHAMBER FORMING AN ENTRAPPING COMPARTMENT OF SUBSTANTIALLY CONSTANT CROSS SECTION EXTENDING A SUBSTANTIAL DISTANCE BEYOND SAID SPARK GAP IN EACH DIRECTION FOR MAINTAINING THE FUEL-AIR MIXTURE SURROUNDING SAID SPARK GAP AT SUBSTANTIALLY BEST POWER MIXTURE WHEN SAID FUEL-AIR MIXTURE IS RICHER THAN BEST POWER MIXTURE, SAID MEMBER WITHIN SAID CHAMBER BEING ADAPTED TO BE LOCATED IN DIFFERENT POSITIONS WITHIN SAID CHAMBER WITHOUT MATERIALLY AFFECTING SAID HEAT RANGE OF SAID SPARK PLUG. 